In 1953 American biologist James Dewey Watson (1928-) and British bio-physicist Francis Crick (1916–2004) developed a model of the structure of DNA (short for deoxyribonucleic acid), the acid found in cell nuclei. The scientists posited that DNA is constructed of a double helix (a spiral ladder) held together by hydrogen bonds. In reaching this conclusion, the pair relied on data gathered by British biophysicist Maurice Wilkins (1916–2004). In the Watson-Crick model, each rung of the DNA ladder consists of two pairs of chemicals. When DNA is replicated (which it is during reproduction), the ladder rungs are divided and the legs form new ladders, identical to the original. The model has helped scientists understand how genetic traits are passed from parent to offspring: Cells in the human body have 46 chromosomes, arranged in 23 pairs; children inherit half a set of chromosomes (threadlike bodies in the nucleus of a cell) from each parent; and different combinations of the parents’ DNA (a process called recombination) produces offspring of different, though related, inherited characteristics. Each person’s genetic information is carried in his or her DNA—between 10 and 20 billion miles of it, which is distributed among trillions of cells in the average human body. The study of DNA’s structure has proved invaluable to scientists working in the fields of evolution, pathology, forensics, and many others. DNA’s “fingerprinting” ability is so powerful that forensic scientists can use the DNA found on a single strand of human hair to identify the owner. In 1962 Watson, Crick, and Wilkins shared the Nobel prize for their groundbreaking work on DNA.